Photometric device.



A. HOWLAND;

PHOTOMETWC DEVICE.

11PPL1cAT1oN man APR.27. 1914.

Patented Mar. 28, 1916.

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A. H'OWLAND.

PHOTOMETRIC DEVICE.

APPLICATION man APRA?. lsu-1,`

Patented Mar. .28, 1916.

2 SHEETS-SHEET 2.

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PHOTDMETRC DEVICE.

LI/lqpyn Specification of Lettere Eatent.

Patented lllan 28, ltllrl. Application led April 27, 1914:. Serial No. 831.@,5573

To all whom t may conce-m: Be it known that l, ARTHUR HOWLAND, a citizen of the United States.. residing at tion. The invention provides means by which such a black, which approximates so closely to an absolute black that it may be considered such for all practical purposes,

Acan be obtained under ordinary and conveniently observable conditions in a light room, as a laboratory, workshop or studio by apparatus contained in a small and convenient compass. By varying the dimensions of the apparatus this approximate giving access to a rather large opening 31 in the front end wall. As here represented the slide has two small observing apertures l2, 13, best seen in Figs. l and 3". llt will be understood that the dimensions of the box may be varied for dillerent purposes, both as to its length, vvhleh determines the depth West Newton, in the county of Middlesex. black, which is black'er than any lack that eo and State of Massachusetts, have invented has ever before been produced under con- ,new md useful Improvements in Photoditions in which it can be mixed With White, metric Devices, of which the following is a so far as l am aware, .can be refinedfurther specification. Y to any desired degree of approximation to llhis invention relates to improvements in the theoretical absolute black. a5 photomgtey f Y The invention is illustrated as it may be More particularly it relates to apparatus embodied in one forni of apparatus, certain for measuring the luminosity of a pigment modifications of which are also shouiii, but or of a surface rellecting light; but it is apthe patent is not limitedy to the particular plicable also to other more or less4 cognate embodiments here illustrated; and it'V is -inim purposes, as, for example, the comparison oi tended t0 Cover by the appended claims pigments for measuring and testing hues Whatever 'features of patentabley novelty and chroma. exist in the invention di closed.

With respect to measurements of lumilu the accompanying drawings, which. nosjty, the Object of the, invention is t0 imrepresent structures embodying the i.nven 7,5 prove upon previously known apparatus in `tion for general laboratory use, Figure l is the' accuracy of results obtainable, especially 21 IOII nfl elmml 0f GHS fOlll O3g lp owing to the high degree of approximation ratus; Fig. 2 is a side elevation; Fig. 3 is of its standards `to absolute correctness and a side elevation on a larger scale in medial the precision with which gradations between section, being on the line 3-3 ol' Fig. l; 30 absolute black or a luminosity of zero, and Fig'. 3 is a plan ,of a detail, in section. on absolute White or a luminosity of one hunlie level 3**81 of Fig. l, enlarged;'lig. l is dred per cent., may be measured. The ima front elevation or' a detail showinga porprovement in accuracy of standards results touof the apparatus by which various grays mainly from` the new standards of black- 0f determinate SlHBCllTCl may l0@ Oblb se which the invention makes possible; and the mGSUTGCl and P1309@ for @Omlm'lson with improvement in precision of measurement 'the GS Sample; F 1g'- 5 is a section on a plane from the method of measuring the ingre- PGYPGDClCUlI O the plane of Fig. l, on li-lie dient proportions of colors or of black and lille 5-5 0f Fg- 4, representing lie parte White in any test sample or in any standard SGPflllil I'ODl llClr Oll; Fig. 5 iS a detail no oilE luminosity for which the apparatus may 0f UlOtllel OHD 0f disk fOl PIGflUCl-Ug f1 be set. standard gray oiu known value; Fig. 7 is still The objects ol the invention are attained. ilIlOlle fOlm 0f the Seme; Fig". 8 sllows a by providing means to utilize, as a standard front elevation, and '9 a side elevation of black, a vista into space from which all of a pair of Maxwell disks Whose lioiut effect e5 light is excluded, and by providing means or mixture is to be compared with the suindfor mixing this black and a standard White 21rd; Figs. l0, ll and l2 represent disks for or any lcolor or colors in precisely measured llflkllgimflilld gllyS of Olilll degrees of proportions in the retinal of the observer, by luminosrtya, and Fig. 123 is a plan of a 1nod1 the spinning process; and further by prollllJlOl, lll SGCOR- l 10o viding means for the comparison of any Referring to the dravymgs, l0 represents standard. gray o'l' -known value thus oba box which 1s light tight, except at the tained, with a surface whose luminosityv is to 'front end, and is preferably lined interiorly be tested, by ocular observation or other- With black velvet, especially at its back Wise under identical conditions of illumina- At the 'front end it is closed by a slide ll, m5

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of vista; and as to its width, and as to the shape, number and dimensions of the openings 1Q', 13. In order to have a sufficient horizontal extent for an opening 19 of convenicnt length or a series of such openings 12 showing standard black. the box 10 may be about twelve inches wide; and I have found in practice that a box of twenty-six inches depth of vista is adequate. The proportions of the box represented in the drawing are somewhat distorted for lack of space. lnteriorly any suitable means such as black, light absorbing vanes 30 are provided for guarding the back surface or end of the vista 22 from illumination by rays entering through the openings 12 or 13.

In using the apparatus under studio or laboratory conditions the box may be placed so that the observer faces the front end of it, as seen in Fig. l, with a window behind him quai-tering to the left, and another be- Ahind him quartering to the right, so that any rays of light entering directly from the window through the opening 12 pass through' obliquely, and impinge first upon the sides of the box or vanes 30. by which they are absorbed or refiected backward and forward, to and fro, until finally they are lost among them or on the edge portions of the back The field toward which the observer looks perpendicularly. is, preferably, a part ofthe back 22 somewhat removed from its edges, and from the shaft 1st. if there be such a shaft in the box. In work requiring exceptional accuracy, rays of light that may enter perpendicularly to the rear wall 22 may be screened as represented (diagrammatieally) at 33, Fig. 3, so that practically no rays can enter the box except those which arrive obliquely. If any of these should reach the back they would strike it at such an angle that they would not be retieeted perpendicularly thence to the eye of the observer.

' ln the form illustrated in Figs. 1.2 and 3. a shaft or axle 14- runs longitudinally through the box.r being journalwl in suitable bearings l5 at the front and 1G at the rear. ln a box of the dimensions stated l' have found that with the apertures lr.) and ll wide open only-a fraction of the length of the shaft is visible. the rear portion being invisible for lack of illumimition: and that any pigment placed against the back surface 22 is absolutely invisible under the eircumstances stated. The presence of the shaft 14 therefore incidentally a tfords a convenient test as to the tightness of the box, for if the shaft should become visible it would indicate the entrance of light in some improper manner. rl`he shaft is arranged to be rotated by any suitable means, here represented as being h v a belt running over pulley 19 outside of thel box and driven by an electric motor l?. The forward and of the shaft is adapted to hold and spin the i, riesce test specimen whose luminosity is to be measured, represented in this case as a pair of Maxwell disks 20, 20, and a white component of the standard of luminosity, the test specimen being observed through the opening 13 and the latter through the opening 12. For the Nmore convenient adaptation ol the apparatus to different purposes the openings 12, 13 are preferably arranged in a thin removable plate il for which other plates may be substituted with holes of other shape or dimension, or with a single hole in place of the two.

The specimen may be either a solid color, or any combination of colors, arranged in any proportions, and including if desired a known proportion of the standard white or of the standard black of the vista, or both. The Maxwell disks represented are shown as being mounted by any suitable means on the end of the shaft 1st. When' the shaft is rotated at a high speed the observer looking through the opening 13 will see the mixture of these colors, which for present purposes may be assumed to be a neutral gray. The standard with which the specimen is to be compared appears through the opening 12. llt consists ot' a mixture of the spinning white of the disk 21, with the stationary black ot' the vista which is indicated in the drawing by theI reference numeral 22 applied to the black velvet back end of the box from which all light that can be reflected to the eye is excluded. Any suitable standard white pigment may be used. Carbonate of magnesia is found suitable for all ordinary purposes: but any pigment having a mat or dead reflecting surface that will serve better as a standard pigment of perfect luminosity may be used if such ever becomes known. Sectors of this disk 21 are excised, and through the excisions the black of the vista is exposed. Preferably these excisions are balanced so that the disk will rotate evenly. The luminosity of the composite standard depends upon the proportion of the white disk left remaining, a complete white disk. having no excised portion, beingA taken as having a luminosity of 100%. A disk whose white sectors cover 1H() degrees of its circumference will have luminosity; and disks whose sectors are of other proportions have a luminosity precisely proportional to the angular arca of white present for observation. This is because that white area constitutes the entire luminosity of the standard, the part excised being replaced, under observation, by the black of the vista Q2, whose luminosity is so close to absolute Zero that the error can be neglected without apf preciable impairment of the'accuracy of the standards obtained while so doing. This black is, indeed, so free from luminosity that the black rotating cards heretofore used as standards of black on the principle of Max- A disk ll oi we standard.. Fig. Li illustrates a means y u* h the luminosity oi the standard may changed, and its precise luminosity read l a scale. ln this case circular scale l is airan fed as a 'iart of the disk` and the possible circumferential extent et the I is divided into four portions, two opposite quadrantsl, 2l being integral with the scale with quadrant excised spaces between them; and lthe remaining two quadrants 2i', 2l being on a` separate disk which can be adjusted either to coincide with said quad rants 21 or to completely lill the spaces tween them, or to .overlap the edges ot the said quadrants and to project partly over the intervening spaces, beside the scale, as illustrated in Fig. l, to any desired degree. ln all such positions the parts `are perfectly balanced about the axle 14. The manner of `tastening the parts on the axle in any relation to each other is clearly shown in F ig. 5 Where the shoulder 24, against which they may-be clamped by the screw nut 25, is seen.

,These parts are accessible `for adjdstrhent 'when the slide 1l is removed. When the disk 2l has been set so that the grays seen through the openings l2, 13 are the saine the position of the disk 21 on the scale 23 will indicate the luminosity. Any suitable means may however be employed to deterlmine the proportions of white and black area in the spinning standard, and this proportion 1s the luminosity. The elements of distance, intensity, size of opening for ad- .mitting light, diil'usion errors for different degrees oit value, etc., do not require consideration nor produce any el'ect vupon the acn curacy of the instrument, for the standard and the test specimen are compared under identical conditions in those respects being lclose beside each other and subject to the daylight,

are so placed that the disks project laterally 'to positions forward of the hole 3l in the `front Wali.y The side walls of the box project still farther forward to support a door 1l', capable of closing the front end ot the v bor, to which it is hinged at l1. Back of this door, and covering the hole 31, is a thin slide having the observation holes 1Q, 13, close in front of the position 'where the disks spin, in this case the vista to the back surtace is provided as ber'ore whenever the door l1 is open. The motor may be mounted above or beside the box in any convenient location, or, as in the other case, some dil'eb ent means of turning tue disks .may be employed. ln either of these styles of construction, and particularlyv in the smaller sizes, the box may take the form of a tube, which, for portability and convenience, may be only three or four inches in diameter and may be materially shorter than an instrunient having wider openings for observation. Tillhcn a motor is used for spinning the disks another adjacent shaft, to wit, the motor shaft, becomes available for spinning disks to mix colors that may be compared simultaneously with the standard, as is indicated by the Maxwell disks and scale portrayed at 20 in Figs. l and 2.

The opening 13 is represented as being fully covered by the test specimen, but it will be obvious that the test specimen might be arranged with excisions so that the black would be mixed with it in any desired proportion. and that many other variations from the precise forni and arrangement chosen to illustrate the invention might be made. ln particular it may be observed that the limitations of the drawing have led to the screen 33 being represented altogether too close to the box. lt would naturally be larger, more remote, and would not limit the rays that pass it to illuminate the apertures 12,13, lto rays of such extreme Obliquity as represented. For all ordinary Work this screen can be omitted Without appreciably impair-ing the accuracy ot' the apparatus; and this ability ot thc apparatus towork under general daylight conditions is one of its advantages. lt Will also be understood that although the arrangement apparatus chosen for illustration shows only a white pigment arranged for spinning with the black, any color or any combination of colors may be substituted for the White, either to make a standard, or for purposes of experiment, test. or com iarison; and that by using suitable dimensions in designing the spinning part and the excisions therein, and the plate 9 and the slide 1l, the black can be introduced as an element in the mixture anywhere in the iield of observation.

In the claims the term pigment is used in a broad sense to signify any kind of surface, reflecting light ot any color. including surfaces ordinarily called White. gray or black; and the term spinning ivhich is the name of one of the most convenient means of mixing colors in the retina of the eye, is used in a somewhat generic sense, as any other means of presenting a rapid repe-` tition of. color impressions to the eye would natu-rally be its equivalent.

I claim as my invention:

l. Photometric apparatus comprising means to form a vista from which light is excluded. whereby an appearance of black is created; a pign'ient ot' maximum luminos-v ity having a measurable extent. arranged between the vista and the point of observation. spinning with measurable intervals through which said black of the vista appears, whereby a standard gray appea ance ot' known luminous value is obtained; and

means to hold another colored body adjacent thereto under identical conditions ot' illumination.

lhotoinetric apparatus `con'iprising means to form a vista from which light is excluded, whereby an appearance of black is created; means to spin a known extent of pigment between the vista and the point ot observation, with measurable inter als through which said black of the vista. appears, whereby a known proportion of black is mixed with the pigment; and means to spin another pigment for comparison` adjacent to the first under identical conditions of illumination.

Photometric apparatus comprising an inclosurc having means to exclude all light except at one end. there being at said end an `opening for observation: means interiorly on the sides of the inclosure to prevent light which enters obliquely through said opening from being reflected by the farther end of the box in the line of observation, whereby said end is in a vist-a having an observed luminosity approximating'zero in value: and means to spin a pigment past saidopening with intervals through which the black ot' the vista appears, thereby mixing thc effect of said black and pigment.

l. Photometrie apparatus comprising a relatively long and narrow inclosure having means to exclude light except at one end. said end having an opening 'for an observer: means lo prevent light entering there from being reflected to the observer; an axle. and pigment disks adapted to be spun thereon. one of the disks having an excision passing said opening.

Photometric apparatus comprising a relatively long and narrow inclosure having means to exclude light except at one end. said end having an opening for an observer: the opposifte end being covered with black material. i nd the sides having transverselyextending. light-interrupting vanes; an axle extending in the. longitudinal direction, and means to hold pigments thereon for spinning past said opening. with intervals through which the luminosity of' the opposite end appears` the surt'ace ot the said opposite end being substantially perpendicular to the line of observation.

6. photometric apparatus comprising relatively long and narrow inclosure.havinI means to exclude light except at one entf said end having an opening for an observer means to prevent light rays entering ob liquely through said opening lroin reachinf theI other end; means to screen said opening; `from light rays that might enter in tlnv longitudinal direction: an excised pigmein disk and means to spin it past said opening and means to hold another pigment adiacent for comparison.-both pigments beim?, similarly illuminated b v oblique rays.

T. photometric apljmratus comprising means to form a vista from which light is excluded. whereby an appearance of black 'is created; a spinning' disk arranged between the vista and the point of ol'iscrvation, having an excision through which the black of the vistamay appear,- a'n'other disk adapted to overlie the tirst and cover to various `de grecs the excision of the first, and..a` scale indicating the degree ot' such overlying.

S. Photometric apparatus comprising stationary means displaying a standard black combined with a spinning pigment having intervals through which the black appears and is mixed as by spinning. and means to hold another colored body adjacent thereto under identical conditions'of illumination.

9. Photometric apparatus comprising stationary means displaying' a color effect, an axle and a pigment disk adapted to be span thereon. arranged adjacent. and having an excision ot measurable extent through Vwhich the said color etlect may pass to the eyeof the observer and thereby appear mixed with the pigment in known proportion, and means to hold another colored body adjacent `thereto ,Y under identical conditions of illumination.

10. Photoinetric apparatus comprising stationary means displaying va ystandard black, an axle and means for holding thereou a plurality of pigment spinning disks exposed at different distances from tbe'axis, includingone havingA an `excision through which the stationary black may appear, whereby a mixture of the stationary black and the pigment ot the disk' may be corn- E pared with an adjacent disk or, mixture 'under similar conditions;

11. photometric apparatus comprising means to form 'a vista from which light is excluded. whereby anappearance of blaelic'is 1' created; a Iscreeny atthe' entrance to said vista having an aperture, a pigment disk having an excifsiorlnand means to spin it by the aperture, conjunction of the aperture and the cxcision"-introducing the black of 1*' the vista as anI element mixed with 'the pig ment over thearea ot the aperture.

12. photometric apparatus comprising means to form a vista from which light is excluded` whereby an appearance of black 1 is created; an apcrtured screen at the entrance to said vista'; means to spin a plurality of disks adjacent thereto, under equal conditions of illumination, one or more hava ing exeisions registering with the aperture,

whereby the said black is mixed with the pigments thereon.

13. Apparatus for making colors of determinate luminosity, comprising the provision of an observable field from which approximately all light is excluded; and means to substitute an illuminated pigment of predetermined luminosity for said eld in the line of observation, for brief intervals with i rapid repetition, during a determinate proportion of the time of observation.

14. .Apparatus for making colors compris- .ing the provision of a stationary field of determinate color quality and means to move another eld of different determinate color quality across the line of observation of the first ield with rapid repetition at intervals .vhose duration bears al determinate ratio to the duration of the crossing.

colors composing the field, each color in the field being arranged in a plurality of portions symmetrical with respect to the center iof rotation whereby the body rotates in balance.

17. Photometric apparatus comprising an inclosure having means to exclude light except at one end, said end having an opening for an observer and the inclo-sure being long in depth from the opening7 relative to the size of the opening; an axle, and pigment disks adazpted to be spun thereon, one

of the diskshaving an excision passing said lopening.

18. Photometric apparatus comprising means to form a vista from Which light is excluded whereby an appearance of black is created; a screen at the entrance to said vista, there being `an opening through the screen, exposing the vista; a pigment disk having an excision; means to spin the disk behind said screen and past said opening, the spinning disk being concealed by the screen, except at the opening, and the con- Yjunction of the opening and the excision introducing the black of the vista as an element mixed With the pigment over the area of the opening.

Signed by me at Boston, Massachusetts.

ARTHUR HOWLAND.

Witnesses:

' ANNA B. LINDSAY,

JOSEPH T. BRENNAN. 

